Combining usually internet or other types of videos whilst some times incorporating music to create a new video that either may be centered around one more themes, or merely to show all of the videos together.

The act of strolling into your local supermarket and heading toward the fruit and veg section. Where you start to masturbate yourself as vigorous as possible, ending with a creamy substance left all over the potatoes, much like Planking became an internet sensation many have taken to Mashing in much the same way.

Andrew: "Look at that girl over there by the tomatoes, she's got her hands right down her knickers."
Richard: "Who? Catherine? Squatting over the Potatoes? She must have her whole fist up there man."
Andrew: "Yeah, she's Mashing hard dude."

Mashing is a term commonly used to describe frotteurism. Frotteurism is a type of paraphilia involving sexual urges or sexually arousing fantasies involving bumping or rubbing against a stranger and/or a nonconsenting person for sexual gratifucation.